1. Field of the Invention
This invention lies in the field of sulfonating acyloxy benzene esters with sulfur trioxide.
2. Prior Art
Knaggs and Nussbaum U.S. Pat. No. 3,169,142 taught a continuous process for sulfation and sulfonation of liquid organic compounds with sulfur trioxide, by contacting a liquid film of an organic compound with a gaseous mixture of sulfur trioxide and inert gas. The resulting product was commonly then neutralized with aqueous base, particularly when making sulfonates having utility as surfactants.
It was appreciated in practicing this process that a small (up to 1.5 weight percent) increase in desired sulfonic acid yield could be obtained in the sulfonation of an alkyl benzene to produce directly the corresponding intermediate sulfonic acid, such as, for example, dodecylbenzene sulfonic acid, by allowing a short holding period to occur between sulfonation and neutralization. This holding period produced such a yield increase because of the reaction of residual quantities of SO.sub.3, present with unreacted alkyl benzene starting feed. No rearrangement is involved.
Esters, such as methyl esters and fatty acid glycerides, are mentioned among many other compounds, in Knaggs and Nussbaum '142 as feedstocks for sulfonation (see col. 3, lines 24-30). In ester sulfonation, the SO.sub.3 apparently preliminarily forms an adduct with the carboxyl group. This adduct can be and preferably is rearrangeable to produce sulfonic acid intermediate products before neutralization. In the case of fatty acid methyl esters, the rearrangement is characteristically endothermic, and alpha sulfonated products result. So far as is now known, no class of esters was previously known whose SO.sub.3 adduct would or could rearrange to produce a ring substituted sulfonic acid.
The practice of the Knaggs and Nussbaum '142 process with ester and other previously employed organic feedstocks characteristically produces side reactions in addition to a main or primary reaction. Thus, it is not easy, and sometimes not even possible, to produce directly by this process high yields of relatively pure sulfated or sulfonated product species, such as is desired and even necessary for many individual and commercial purposes. Terminal purification procedures are sometimes necessary in order to obtain sulfonated products of a desired purity. Such purification procedures are undesired since they add to the cost of making a product.
Recently, it has been proposed to use acyloxy benzene sulfonate compounds, of the class wherein the acyl group is derived from a fatty acid, in commercial detergent formulations. Large-scale usage appears to require a synthetic route for making such compounds which is inexpensive and capable of producing a relatively high purity product in high yield.
The indicated Knaggs and Nussbaum process would at first appear to offer promise as a potentially inexpensive synthetic route for making these compounds by sulfonating the corresponding phenyl ester. So far as is now known, no one has previously prepared acyloxy benzene sulfonate by direct synthesis with SO.sub.3 from acyloxy benzene. However, when one attempts to practice such '142 patent teachings of Knaggs and Nussbaum to sulfonate an acyloxy benzene, various formidable unexpected problems arise, some of which appear never heretofore to have been experienced in SO.sub.3 sulfonation of organic compounds, especially esters. These problems result in yields of acyloxy benzene sulfonates that are so low as not to be of apparent commercial practicality or feasibility. Further, the desired product is accompanied by significant quantities of unwanted by-products, for example, sulfones and phenolic materials, which detract even further from the commercial value or practicality of using such so-produced acyloxy benzene sulfonates in surfactant formulations.
One of the yield-reducing problems which can arise when sulfonating is the occurrence of degradation which is undesired and which results from the reactivity of the sulfur trioxide with acyloxy benzene. Degradation not only reduces the yield of the desired acyloxy benzene sulfonate, but also produces by-products which adversely affect desired product characteristics, such as color and shelf-life stability.
Moreover, if one attempts to follow prior art teachings as regards use of a heated digestion zone between sulfonation and neutralization, then both side reactions and degradation problems are compounded and yields of acyloxy benzene sulfonate go down. Thus, the sulfonation process taught by the Knaggs and Nussbaum 142 patent is not suitable for directly making acyloxy benzene sulfonates of commercially acceptable quality and purity. At the least, it appears that with this process some sort of a special terminal "clean-up" step would be needed to produce a light color product with a content of acyloxy benzene sulfonate above about 70 weight percent (total product solids weight basis). However, such "clean-up" step would only undesirably add to the cost of making the final product.
Apart from the foregoing considerations with regard to sulfonation, the prior art has heretofore appreciated that the conditions employed in neutralization of an organosulfonic acid ester can affect yields of the resulting desired product salt. For example, unless the temperature and the pH at which neutralization is accomplished with a material such a sulfonic acid of an aliphatic carboxylic acid ester are controlled, such as, for example, an alpha sulfo methyl fatty acid ester, one can wind up with a neutralized product which is substantially hydrolyzed. In the case of neutralizing acyloxy benzene sulfonate acid, control of neutralization using special conditions is necessary in order to avoid hydrolysis of this acid.
Thus, the prior art does not provide any sulfonation process which permits one to produce acyloxy benzene sulfonates in high yield and in high purity.